[API Review for 1.1] Hash-Array Mapped Prefix Trees

[tera]

+1 for "Big", same reasoning.

@kiel

Could this functionality be accessed through special initialisers on those existing types and therefore avoid the naming problem -- or confine it to an initialiser?

+1 for the hint parameter to normal Dictionary / Set.

And for data structures that allow accessing previous versions names "VersionedSet" / "VersionedDictionary" sound reasonable.